PROJECT SUMMARY. Many patients with advanced prostate cancer along with their decision partners/ proxies (DPP) struggle with complex treatment decisions, such as when to start, change, or stop cancer directed treatment. Despite the utility of decision aids (DAs) to address decisional conflict, little is known about treatment decision-making for advanced cancers. The study's primary aim is to test the effects of a theory- based mHealth DA (CHAMPION) administered by Registered Nurse (RN)-Community Patient Navigator (CPN) teams to advanced prostate cancer patients and decision partners/proxies on the following outcomes: less decisional conflict/uncertainty, higher psychosocial quality of life domain (HRQL-PSY), and less regret at the time of making an anti-cancer treatment decision. The secondary aim is to evaluate the CPN role in delivery of the mHealth DA (CHAMPION) from the patients' and decision partners/proxies' perspective. Preliminary estimates of treatment effects by race to see if the data support a larger effect among African Americans versus Others in the primary and secondary aims will also be explored. This mixed-methods population-based randomized controlled trial will gather data from 158 patient/DPP pairs at three sites: University of Virginia Emily Couric Cancer Center, the Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins University, and Virginia Commonwealth University Massey Cancer Center. The pretest/posttest design will measure a time period that includes three single-event decisions over the course of their cancer-directed treatment; and a qualitative retrospective design will allow exploring the experiences of both patients and their DPPs separately in an interview at the completion of the study. Stratification by race (African-American and Caucasian/Other) and decision point (starting vs. changing vs. stopping anticancer treatment) will be used. There will be two groups: the control (enhanced usual care [EUC]) group and the decision intervention (DI) group. The DI group will receive an interactive 7-component cognitive-behavioral skills mHealth program (DA) with a RN-CPN team, primarily focusing on decision-making during cancer treatment. Self-report measures will be used for all participants in addition to probes for the taped interviews with DI. The primary outcome measures are 1) decisional conflict (uncertainty), 2) decisional regret, 3) HRQL-PSY, and 4) decision-making participation preference. Generalized linear models will be used for data analysis for the quantitative component, and qualitative evaluation of the intervention will be conducted to capture each pair's experience of the CHAMPION intervention. This innovative mHealth DA delivered by a CPN is expected to increase acceptability and the uptake of both the DA and the technology components. This addresses several NIH/NINR innovative questions, through the use of information technology to promote health-related decision-making for providers and patients, examining patient outcomes for improvement in healthcare, as well as to engage and support individuals such as extended family, lay coaches, etc. to augment provider care and recommendations.